#include /* factorial Formal Definition: n! = 1*2*3*...*n */ // templatized templatestruct Factorial{ static const uint64_t result = N * Factorial::result ; }; template<>struct Factorial<0>{ static const uint64_t result = 1; }; // recursive uint64_t rFactorial( uint64_t n ){ if ( 0 == n ) return 1; return n * rFactorial( n - 1 ); } // loop uint64_t getFactorial( uint64_t n ){ uint64_t result = 1; while ( n ) result *= n--; return result ; } #include #include #include #include // build table using Data = std::pair; std::vector buildTable( int x ){ std::vector table; for ( int i = 0 ; i < x ; ++i ) table.push_back ( std::make_pair( getFactorial( i ) , i ) ); std::sort( table.begin() , table.end() , []( Data x , Data y ){ return x.first < y.first; } ); return table ; } #include void printCompare( std::vector table ){ std::cout << " * * Factorial(n) result table loop vs recursion * *\n" << "input" << std::setw(17) << std::right << "loop" << std::setw(14) << std::right << "rec\n"; for ( auto i : table ){ std::cout << std::setw(3) << std::right << i.second << "! : " << std::setw(15) << std::right << i.first << std::setw(13) << std::right << rFactorial( i.second ) << "\n"; } } using namespace std; int main() { cout << "Factorial(20)\n" << " * compile time<> : " << Factorial<20>::result << "\n * runtime recursion : " << rFactorial(20) << "\n * runtime loop : " << getFactorial(20) << endl << endl; vector table = buildTable( 15 ); printCompare( table ); return 0; }

Algorithms [Jhon Wells] factorial